CONICET | Buscador de Institutos y Recursos Humanos

Upper Cambrian Lower Ordovician strata of the South American Central Andean Basin contain abundant and well preserved trace fossils assemblages that have been mostly treated after 1970 (Borrello, 1966; Ramos, 1973; Aceñolaza, 1978; Alonso and Marquillas, 1981; Toro et al., 1988, 1990; Mángano et al., 2001; Aceñolaza and Aceñolaza, 2002 with references). These studies were preceded by few early papers where the ichnological richness of the region could be previewed (e.g. D´Orbigny, 1842). The last mentioned author described Bolivian material from the surroundings of Zudañez (Cochabamba and Chuquisaca departments), introducing Cruziana, an ichnogenus that nowadays is one of the most remarkable trace fossils. Lower Paleozoic Cruziana is mostly regarded as a trilobite crawling exite-produced trace, and due to its striking morphology has provoked many remarkable papers focusing different aspects related to its production, preservation and variability (e.g. Seilacher and Crimes, 1969; Crimes, 1970; 1975; Seilacher, 1970; Crimes and Marcos, 1976; Bergström, 1976; 1979; 1981; Pickerill and Fillion, 1983; Fillion and Pickerill, 1990). Outstanding Cruziana pavements have been recently localized in the Lower Ordovician strata of the Sierra de Zenta of Jujuy province (northwest Argentina). Traces are mostly assigned to the "rugosa group" of Seilacher (1970), and were found in the upper sector of the Santa Victoria Group close to the Abra Blanca locality of the Sierra de Zenta. Traces are preserved as positive hyporelief produced by casting on sand of previously excavated layers and as rare negative epireliefs in the upper surface of strata. The preservation of very fine morphological details, as claw and exite marks, are a result of the interaction of the particular paleoenvironmental conditions of sequences (e.g. environmental energy, substrate coherence, water content of sediments) and the ethology of the producer organism. The objective of this paper is to present this outstanding new ichnofossiliferous locality, advancing some results of an interdisciplinary project that is being carried out in the Sierra de Zenta of northwest Argentina.

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